Amplitude discrimination is predictably affected by echo frequency filtering in wideband echolocating bats

Big brown bats emit wideband frequency modulated (FM) ultrasonic pulses for echolocation. They perceive target range from echo delay and target size from echo amplitude. Their sounds contain two prominent down-sweeping harmonic sweeps (FM1, ~55-22 kHz; FM2, ~100-55 kHz), which are affected differently by propagation out to the target and back to the bat. FM2 is attenuated more than FM1 during propagation. Bats anchor target ranging asymmetrically on the low frequencies in FM1, while FM2 only contributes if FM1 is present as well. These experiments tested whether the bat's ability to discriminate target size from the amplitude of echoes is affected by selectively attenuating upper or lower frequencies. Bats were trained to perform an echo amplitude discrimination task with virtual echo targets 83 cm away. While echo delay was held constant and echo amplitude was varied to estimate threshold, either lower FM1 frequencies or higher FM2 frequencies were attenuated. The results parallel effects seen in echo delay experiments; bats' performance was significantly poorer when the lower frequencies in echoes were attenuated, compared to higher frequencies. The bat's ability to distinguish between virtual targets at the same simulated range from echoes arriving at the same delay indicates a high level of focused attention for perceptual isolation of one and suppression of the other.

The Impact of Auditory White Noise on Cognitive Performance

Although noise has often been characterized as a distractor, contemporary studies have emphasized how some individuals’ cognitive performance could benefit from task-irrelevant noise. Usually these studies focus on sub-attentive individuals and/or those who have been diagnosed with ADHD. An example of task-irrelevant noise is white noise (WN). Research regarding the effectiveness of WN in healthy adults has provided mixed results and therefore, the implications of WN remain unknown. The objective of this study was to determine the effects of WN on the cognitive performance of the neurotypical population. To test this, participants were asked to complete simultaneous amplitude discrimination and temporal order judgement (TOJ) tests several times in the presence of varying levels of WN. Participants were split into two groups––one containing individuals with regular prior WN exposure and the other with no previous experience with WN. The performances of participants with prior exposure to WN, but not those without prior exposure, resembled a U-shaped tuning curve for simultaneous amplitude discrimination. This indicates that familiarity with WN moderates its effectiveness on cognitive improvement. TOJ was not found to be affected by varying levels of WN intensity. The results of this study emphasized that there is a possibility that WN could facilitate higher levels of cognitive performance, though there is likely an adjustment period associated with its introduction to daily life. This warrants that additional research should be conducted in order to cultivate a definitive conclusion about the effects of WN.

Muon Tracker with Unsegmented Plastic Scintillator Panels

A muon tracker was developed using three polyvinyl toluene scintillator panels instrumented with photomultiplier tubes (PMTs) mounted at the corners. Panels are mounted in parallel on an aluminum frame which allows for simple adjustment of angle, orientation and separation distance between the panels. The responses of all PMTs in the system are digitized simultaneously at sub-nanosecond sample spacing. Software was developed to adjust settings and implement event rejection based on the number of panels that detected a scintillation event within a 400-nanosecond record. The relative responses of the PMTs are used to calculate the position of scintillation events within each panel. The direction of the muons through the system can be tracked using the panel strike order. Methods for triangulation by both time-of-flight (TOF) and PMT magnitude response are reported. The time triangulation method is derived and experimentally demonstrated using parallel cables of differing length. The PMTs used in this experiment are only optimized for amplitude discrimination, not for time spread jitter as would be required to implement TOF methods into the scintillator panels. A Gaussian process regression machine learning tool was implemented to learn the relationship between PMT response features and positions from a calibration dataset. Resolution is analyzed using different numbers of PMTs and low-versus-high PMT sensitivities. Muons traveling in forward and reverse directions through the detector system were counted in all six axis orientations. The muon detector was deployed for 28 days in an underground tunnel and vertical muon counts were recorded.

Lateral Inhibition: Are two hands better than one?

This study investigated the differences in amplitude discrimination capacity between two stimuli delivered to adjacent fingertips on the same hand (contralateral delivery) and stimuli delivered to two fingers on opposite hands (bilateral delivery). The measures were obtained in order to study the impact of lateral inhibition via interhemispheric connections on cortical centers on opposite sides of the somatosensory cortex in comparison to lateral inhibition occurring between adjacent cortical centers within the same hemisphere. Using the Cortical Metrics Brain Gauge™ device, amplitude discrimination capacity of 37 healthy subjects was assessed at several different durations, ranging from 40 to 500 msec, of vibrotactile stimulation delivered contralaterally and bilaterally. The results demonstrate a significant difference in amplitude discrimination capacity between the two conditions for stimulus duration of 200ms, with performance being better for the contralateral delivery of the stimuli than the bilateral condition for most tested durations. Task performance was roughly the same for the two conditions at the extremes of short (40ms) and long (500ms) stimulus durations. Amplitude discrimination capacity improved with longer stimulus durations in both bilateral and contralateral conditions. Though slight variation was observed at the level of each individual subject, overall, it is clear that local lateral inhibition plays a role in assessing the two stimuli delivered to the same hand that gives same-handed discrimination an advantage over two-handed discrimination. Additionally, the trends identified may be useful in guiding future experimentation that investigates clinical assessments of deficits in cortical processing that is mediated by callosal connections.

An Experimental Animal Model that Parallels Neurosensory Assessments of Concussion

ABSTRACT Introduction Tactile-based quantitative sensory assessments have proven successful in differentiating concussed vs. non-concussed individuals. One potential advantage of this methodology is that an experimental animal model can be used to obtain neurophysiological recordings of the neural activity in the somatosensory cortex evoked in response to the same tactile stimuli that are used in human sensory assessments and establish parallels between various metrics of stimulus-evoked cortical activity and perception of the stimulus attributes. Materials and Methods Stimulus-evoked neural activity was recorded via extracellular microelectrodes in rat primary somatosensory cortex (S1) in response to vibrotactile stimuli that are used in two particular human sensory assessments (reaction time (RT) and amplitude discrimination). Experiments were conducted on healthy control and brain-injured (BI) rats. Results Similar to the effects of mild traumatic brain injuries (mTBI) on human neurosensory assessments, comparable experimentally induced brain injuries in rats resulted in the following: (1) elevation of S1 responsivity to vibrotactile stimulation that depended nonlinearly on stimulus amplitude, significantly reducing its capacity to discriminate between stimuli of different amplitudes; (2) 50% reduction in S1 signal-to-noise ratios, which can be expected to contribute to elevation of RT in BI rats; and (3) 60% increase in intertrial variability of S1 responses to vibrotactile stimulation, which can be expected to contribute to elevation of RT variability in BI rats. Conclusions The results demonstrate suggestive similarities between neurophysiological observations made in the experimental rat mTBI model and observations made in post-concussion individuals with regard to three sensory assessment metrics (amplitude discrimination, RT, and RT variability). This is the first successful model that demonstrates that perceptual metrics obtained from human individuals are impacted by mTBI in a manner consistent with neurophysiological observations obtained from rat S1.

Response Time in Somatosensory Discrimination Tasks is Sensitive to Neurological Insult

Background: A number of reports have demonstrated significant differences in human performance on diverse somatosensory-based discriminatory tasks dependent on the individual’s neurological status. For example, compromised neurological status has been shown to lead to poor performance on tactile-based tasks such as vibrotactile stimulus amplitude discrimination, frequency discrimination, temporal order judgement, timing perception, and reaction time, and these deficits have been observed across a diverse spectrum of neurological disorders. Results: In this report, response time of recently concussed individuals (1-3 days) was found to be significantly longer (~25%) than that of non-concussed individuals (i.e., controls) and individuals recovering from concussion (10+ days post-concussion). Additionally, a significant difference was found in response time on two different tasks. Timing perception, which is hypothesized to engage significantly more neural circuitry than amplitude discrimination, had a significantly longer average response time than amplitude discrimination. Conclusions: These findings strongly suggest that response time could be used as a discriminative measure when evaluating overall neurological health and/or cognitive function, and this is consistent with findings of other reports that examined speed-accuracy trade-offs on discrimination tasks.